A line lamp in prior art connects serially a plurality of halogen lamps on a main electric line that is used to conduct electricity. There is no robust protection for the lamp socket and the lamp of the halogen lamp. The halogen lamp will shed if it can not be locked on the lamp socket. To improve this situation, a retaining frame is installed to enhance the lamp socket such that the main electric line connects with the lamp socket via an adapting electric line, and a protection lid is installed on a retaining seat to protect the lamp. But it is very inconvenient to replace the lamp for this structure.